Filter benign unobserved-Task socket noise from Sentry (BL-16573)

[hatton]

[Claude Fable 5]

Screens out the benign "unobserved Task socket/IO abort" noise that the Sentry .NET SDK reports on our behalf. Three locale-split Sentry issues share one root cause and together account for ~71,000 events / 0 users over 90 days:

• BLOOM-DESKTOP-EQ4
• BLOOM-DESKTOP-E4J (Spanish-locale variant)
• BLOOM-DESKTOP-E9K

Root cause

The Sentry SDK auto-subscribes to TaskScheduler.UnobservedTaskException. Fleck (our WebSocket library, behind BloomWebSocketServer) does fire-and-forget socket.Send() calls whose faulted Tasks are never observed; when a socket aborts (mostly at app shutdown) the finalizer thread surfaces a benign SocketException/IOException and Sentry reports it. As Sentry serializes it, the event is an inner System.Net.Sockets.SocketException ("The I/O operation has been aborted...") wrapped in a System.AggregateException whose mechanism is UnobservedTaskException. An earlier IsAvailable-check mitigation (BL-11124) did not stop it.

Fix

Switch SentrySdk.Init to the Action<SentryOptions> overload (same DSN) and add a narrowly-scoped BeforeSend filter that drops ONLY this pattern: an event carrying the UnobservedTaskException mechanism whose exception chain contains a benign socket/IO abort type. The decision is carried by exception type + mechanism, never by message text, so it is locale-independent and covers all three issues (and future language variants) at once.

Genuine unobserved-Task bugs are still reported - we deliberately do NOT call DisableTaskUnobservedTaskExceptionCapture(). The filter predicate is a testable internal static method with unit tests in BloomTests covering a matching event (dropped), the localized-message (Spanish) variant, and non-matching events (passed through).

Ref: https://issues.bloomlibrary.org/youtrack/issue/BL-16573

🤖 Generated with Claude Code

Devin review

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This change is 

[greptile-apps]

Greptile Summary

Adds a narrowly-scoped BeforeSend Sentry filter that drops the benign "unobserved Task socket/IO abort" noise (three Sentry issues, ~71k events, 0 users) caused by Fleck's fire-and-forget socket.Send() calls surfacing as unobserved SocketException/IOException/cancellation at shutdown — without disabling the broader UnobservedTaskException integration.

• IsBenignUnobservedTaskSocketNoise gates on both the UnobservedTaskException mechanism and the presence of only benign exception types, so genuine unobserved-Task bugs and mixed-fault AggregateExceptions are still reported.
• Eight NUnit tests cover all four benign-type branches (drop), mixed chains containing a real bug (keep), the vacuous-All guard, mechanism-absent SocketException, and the empty-event edge case — including a parameterized case added post-initial-review for the two cancellation types.

Important Files Changed

Filename	Overview
src/BloomExe/Program.cs	Adds two well-commented helper methods for Sentry noise filtering and switches SentrySdk.Init to the options overload with a narrowly-scoped BeforeSend filter; logic is correct and safe-fails on unexpected shapes
src/BloomTests/ProgramTests.cs	Adds 8 parameterized and standalone NUnit tests covering all four benign-type branches (drop), mixed chains with real bugs (keep), vacuous-truth guard, mechanism-absent case, and the empty-event edge case

_{Reviews (3): Last reviewed commit: "Merge remote-tracking branch 'origin/mas..." | Re-trigger Greptile}

[hatton]

[Claude Fable 5] Consulted Devin on 2026-07-18 19:22 up to commit c81bb65 (re-review after the review-follow-up commit).

Result: 0 bugs, 1 Investigate, 1 Informational — the same AggregateException-unwrapping Investigate flag as the prior review, which is already posted as an inline thread, refuted with a real captured event, and resolved; skipped re-posting per dedup. Greptile re-review passed with no new findings; both earlier Greptile P2 items are addressed and resolved. CI green. Re-review clean — bots quiet.

[JohnThomson]

[Claude Fable 5] Consulted Devin on 2026-07-23 up to commit d39376a (re-review after tightening the benign-type check from Any to All).

Result: 0 bugs, 1 Investigate, 2 Informational. The Investigate flag is the same AggregateException-unwrapping question raised on the previous commit — its thread already has the answer (verified against a real captured event on BLOOM-DESKTOP-EQ4: the wrapper and its mechanism survive to BeforeSend in the SDK version we ship) and is resolved. The two Informational notes restate trade-offs already documented in code comments (the breadth of the benign type set, and BeforeSend applying to the whole pipeline but being scoped by the mechanism check). No new findings to mirror.

[JohnThomson]

@JohnThomson+AGNT resolved 1 discussion.
Reviewable status: 0 of 2 files reviewed, all discussions resolved (waiting on hatton).